Fixes #1066 This PR adds a new field `access` in the transportation layer, which will be set to `no` if the `access` tag is either `no` or `private`. While `private` is the more popular value by a 17:1 ratio, I went with `no` because it's smaller in the tiles. In addition, the text `no` opens up the future possibility of other text-based access values such as `destination`, `customers`, or `permit`. The screenshot below shows an example of access tagging for a road on a military base: 
transportation
Docs
Read the layer documentation at http://openmaptiles.org/schema#transportation

